I've been building things around my house using SI, and it's not that
tough. Yes, it would be better if all the lumber were in rational metric
sizes, but it doesn't really matter much. No piece of lumber is exactly
what it's supposed to be, so I've never been able to assume that a piece of
nominal 1x3 would actually be 2 1/2" wide. I've always had to measure it.
If I measure it as 2 7/16" or 62mm, it's the same width, except that "62mm"
is easier for me to scribble on my construction notes.
As for the difficulties of dividing a 4' x 8' panel into three for the
placement of studs (nominal 16" centers) using SI, this is also largely an
illusory problem. A nominally 4' panel -- if it is truly 4' wide -- would
be 1219.2mm wide. The 0.2mm is completely inconsequential; if I drag the
panel across the garage floor I'm likely to rub off that much on the
concrete, so it's not worth worrying about. So that leaves the panel width
as 1219mm, which looks like a pretty ugly number to divide by 3, but it's
not. Dividing it by 3 gives 46mm with a remainder of 1mm. I can ignore the
remainder because it's only about the thickness of a US dime. There's not
much house construction that is built to the precision of the thickness of
a dime! I'm very lucky if I can achieve millimeter-precision in my woodworking.
I find that a lot of the problems of working with building products made to
hard-inch dimensions while using SI vanish when I keep in mind the level of
precision required or possible. A millimeter here or there simply doesn't
matter in most cases.
I do appreciate it that having inch-sized building products does make
building in SI a mental challenge (you have to get over worrying about a
millimeter here and there), but I'm puzzled that this was an insurmountable
problem for the Michigan road construction industry. What's the level of
precision used in pouring concrete slabs or laying asphalt? What's the
level of precision involved in bending reinforcing bar, binding it together
with rebar tie-wire, and imbedding it inconcrete? Who's using telescopic
rifle sights to lob water balloons?
